Labour's election hopes have taken a double blow with today's Stuff.co.nz-Ipsos poll showing its support at a caucus-savaging 23 per cent and fresh questions about David Cunliffe's leadership.

OPINION:
Former leader David Shearer was rolled the day after an earlier Stuff poll put the party at 31.6 per cent and that has sparked questions about whether Cunliffe will suffer a similar fate.

The latest poll, which has National at a gravity-defying 56.5 per cent, comes less than a day after it emerged Cunliffe wrote a letter on behalf of wealthy businessman Donghua Liu despite his earlier denials.

Labour MPs were clearly shattered by yesterday's revelations, although Cunliffe continued to deny he had done anything wrong.

Even his caucus opponents stopped short of calling for a spill, saying it was too close to the election to contemplate a change - but also because there was unlikely to be anyone prepared to step up.

Labour's constitution allows the usual party-wide vote and a primary run-off for leadership to be set aside within 90 days of the election, leaving it in the hands of its 34 MPs.

But insiders said that could spark a civil war within the party, which elected Cunliffe without the backing of a majority of its MPs.

However, that was before today's morale-sapping poll which will bring back memories of 2002 when National was seen as doomed and voters deserted it in droves, leaving it with just 21 per cent of the vote and a shrunken caucus of just 27 MPs.

There are indications of the same effect in today's survey, with a big move away from Labour towards the half-way house of "undecided".

As yet there is no sign of minor parties benefiting, with the Greens and NZ First down slightly, although the embryonic Internet-Mana nudged up to 2.1 per cent - enough for three MPs.

It is a depressing picture for Labour, just 93 days out from an election it was already at long odds to win.

It's hard to believe things could get much worse for Cunliffe and his party, although National is hinting more damning revelations about Liu's donations to Labour will soon see the light of day.